Power Line Communication (PLC) is becoming a popular network technology in the consumer electronics market since the existing electrical wiring of a house is used for data traffic without need for separate data wiring. PLC networks also do not have the security issues of wireless networks. Quite a few products including, but not limited to, bridges, routers and other products are currently commercially available from several manufacturers in the consumer market.
At this writing, the current PLC technology employs the technologies of OFDM (Orthogonal Frequency Division Multiplex) and CSMA/CA (Carrier Sense Multiple Access with Collision Avoidance. OFDM is a known modulation scheme that uses multiple carriers in a spread spectrum transmission scheme to transmit information. CSMA/CA is a known channel access protocol that is used in Ethernet. In such PLC systems, transmitters and receivers exchange information that identifies available/usable carriers (called a “tone map”) every several seconds. Some carriers cannot be used because of noise interference (e.g., from motors, switching power regulators and other sources of electrical interference). The transmitter transmits data using the available carriers and leaves the others unused.
The operation of the CSMA/CA channel access mechanism is as follows. Before the transmitter starts a transmission, the transmitter first detects the network bus. If the bus is not busy, the transmitter starts transmission. When the bus is busy, the transmitter re-tries transmission after a random waiting time.